Cell Membranes

Active transport  -  The transport of molecules across a membrane and against their natural flow; mediated by carrier proteins and requiring outside energy.

Carrier protein  -  A protein responsible for mediating the active transport of molecules from one side of the lipid bilayer to the other. Transport is carried out by a conformational change that occurs within the protein that forms an opening for specific molecules to pass through.

Channel protein  -  A protein responsible for mediating the passive transport of molecules from one side of the lipid bilayer to the other. Transport is carried out by its membrane-spanning hydrophilic structure which, when open, allows molecules to pass through.

Diffusion  -  The transport process in which molecules naturally travel from an area of higher concentration to an area of lower concentration.

Glycocalyx  -  A layer of carbohydrates that coats the exterior of higher-ordered cells. Functions in protecting the cell from damage.

Hydrophilic  -  A polar molecule that selectively associates itself with water through hydrogen bonds.

Hydrophobic  -  A nonpolar molecule that does not readily associate with water through hydrogen bonds.

Integral protein  -  A membrane protein that cannot be easily removed from the lipid bilayer.

Ionophore  -  A class of membrane transport proteins. Small, hydrophobic molecules that increase membrane permeability to certain ions.

Lipid bilayer  -  A thin double layer of phospholipid molecules. Provides the structure of a cell membrane. Structure is a result of hydrophobic and hydrophilic forces.

Lipid-bound protein  -  Membrane proteins that are located entirely within the lipid bilayer, having no part touching either the inside or outside of the cell.

Multi-pass protein  -  Transmembrane proteins that cross the lipid bilayer more than one time.

Osmosis  -  The process by which water naturally travels from an area of high concentration to one of lower concentration.

Passive transport  -  Transport mediated by channel proteins. The movement of molecules across a membrane according to the natural flow.

Peripheral protein  -  A membrane protein that can be easily removed from the lipid bilayer.

Single-pass protein  -  A transmembrane protein that only crosses the lipid bilayer one time.

Transmembrane protein  -  A membrane protein that spans the lipid bilayer having portions in contact with both the inside and outside of the cell. Area within the lipid bilayer forms an alpha-helix.